It has been a long known practice to ventilate attics under gable roofs by running a vent along the roof ridge. Such vents are created by an open slot running along the roof ridge, essentially the length of the roof, which causes ventilation out of the attic by convection airflow and by suction from wind blowing across the roof.
A soffit ventilation system is frequently used in conjunction with a ridge vent to provide passive ventilation. The soffit vents allow fresh ambient air to flow into the attic to equalize attic temperature and pressure with the outside. As stale hot air is withdrawn from the ridge slot vent by convection and/or wind suction, it is replaced by fresh ambient air entering the attic through the soffit vents.
The effectiveness of the ridge vent depends upon the degree to which convection outflow and wind across the vent line is uninhibited by the vent structure. Most effective would be a completely uncovered slot, but the need to keep out rain water, dirt and pests requires some sort of covering or capping structure. Design consideration for a vent structure includes, therefore, an attempt to maximize convection and suction outflow while establishing an effective barrier against water, dirt and insect entry, creating or maintaining an aesthetic appearance of the roof, long term durability, low cost construction, and ease of installation.
Differences between the various types of ridge vents are often found in the capping structures used over the vent slot. A description of representative types of ridge vents and capping structures, and attributes or problems associated with various types, is found in a prior patent of this inventor, U.S. Pat. No. 5,167,579 (Rotter). That patent discloses, as a solution to many of the problems associated with prior ridge vents, an improved roof ridge venting system using a unitary mat constructed of randomly-aligned synthetic fibers which are joined by phenolic or latex binding agents and heat cured to provide an air-permeable mat with a varying mesh. Cap shingles are supported by the mat and are nailed directly to the roof through the mat. In contrast to other vent materials, the unique features of the mat disclosed in the Rotter patent result in many desirable physical properties such as high tensile strength, high resiliency, the ability to be transported in rolls and cut to length, ease of joining strips, durability in local ambient conditions, and an excellent water and insect barrier. Moreover, it provides the aforementioned desirable features in a thin sheet to permit the vent structure to maintain a low profile along the roof.
Although the vent disclosed in the Rotter patent has desirable applications in many roof types, some of its advantages begin to diminish when it is used in conjunction with metal roofs. Metal roofs panels have a high thermal conductivity and therefore expand and contract with temperature changes during the day and through the seasons. In addition, metal roofs are typically formed of panels having stiffening ribs in which the stiffening rib in proximity to one lateral edge overlaps the stiffening rib in proximity to the other lateral edge of the adjoining panel. It is therefore difficult to create a vent for the passage of air at the ridge while preventing space through which bugs and moisture can pass. It is therefore more common to have ventilation cans on the metal roof, or wall vents located on gable ends of the building rather than ridge vents on metal roofs.
U.S. Pat. No. 5,352,154 (Rotter, et al.) describes a clip that are disposed at intervals on each of the standing seams. A plurality of air-permeable venting material section extend between adjacent clips on one side of the open slot and substantially fill the channels in the clips. A ridge cap overlies the venting material sections and spans the open slot. One shortcoming of this method of using the clips is that the installation is very labor intensive with each clip having to be installed individual and each section of venting material. Furthermore, the planar construction of the mat in the '154 patent does not lend itself to being used with panels having continues corrugation curves.
If is desired to have a structure and method of venting ridges of metal roofs having stiffening ribs which is effective and not labor intensive and capable of working with continues corrugation curves.